The present invention relates to ultrasonic diagnostic equipment. In particular, the invention relates to a hand-held array of ultrasonic transducers which are positioned over the object, such as a human body, to be examined and to the associated signal producing, processing and display equipment which provides the operator with an output indicative of the cross section of the body below the hand-held device. Although ultrasonic diagnostic equipment has been used for several years, the present invention is an improvement over previous units because it has much greater versatility, resolution, and freedom from distortion.
Twice the horizontal resolution of the earlier units is made possible in the present invention by using a unique method of actuating odd and even numbers of transducer elements. This method provides twice as many lines of data for each view of the object examined.
To reduce spurious signals resulting from grating-lobe responses, the present invention uses a novel structure for transducer elements. Each transducer element is divided in half or comprised of two transducer elements coupled in parallel at each transducer element position. This parallel transducer arrangement achieves a significant reduction in spurious responses.
The present invention provides for more precise focusing than previous machines. One way is by allowing the user to select any one of a number of apertures, i.e. select the number of transducer elements which will be pulsed as a group. By making the size of the aperture variable, the present machine has better resolution at both shallow and deep depths. Because pulsing larger numbers of transducer elements per group will produce the best focusing and depth of field at greater depths within the object to be examined, whereas pulsing a relatively small number of transducer elements will produce the best focusing at depths closer to the surface of the object being examined, previous fixed aperture machines are not able to match the present resolution over the full shallow to deep range. Although others have devised transducer probes which actuate different numbers of transducer elements at the same time, for example see U.S. Pat. No. 3,911,730, the invention herein recognizes the relationship between the length (number) of the group of transducer elements pulsed and the focus of the resulting picture at the depth of interest.
Another way in which the focusing is improved is by shaping the transmitted signal from the ultrasonic probe into a generally arc-like wave which converges at the depth of interest by using a number of delay circuits to modify the relative actuation time of each element within the group of transducers being activated in such a manner that each point on the resulting wave front reaches a point at the depth of interest at the same time. U.S. Pat. No. 3,919,683 illustrates the use of delay circuits to help focus the wave front, but unlike the present invention it requires a separate delay circuit for every pair of elements within each group of transducers. The present invention does not use a fixed ratio of delay circuits to elements within the group. Instead it recognizes that a small number of delay circuits which can be programmed for different delay periods can produce the same results with less hardware, i.e. cost.
Analogously, the present invention uses small numbers of programmable delay circuits to bring echo signals received by the transducer elements into coincidence before processing them to form the visual display.
Simplification of the post processing of the echo signals is achieved by using a log compression system. In the log compression system, the amplitudes of the echo signals are transformed into their logarithmic equivalents. This allows the system to handle a wide echodynamic range and reduces the equipment necessary to transform these signals into a video picture. Logarithmic intensity modulation circuits per se are not new, for example see U.S. Pat. No. 3,881,466 which uses logarithmic intensity modulation circuitry in conjunction with an oscilloscope display.
Another unique feature of the present invention is its display format. The display is such that it can be produced on a standard TV screen. This is accomplished first because the invention doubles the number of data lines produced without increasing the number of transducer elements, and second because the interpolation system of the present invention increases the number of data lines still more. In this manner, a small hand-held array, such as one with sixty-four transducer elements, can produce a sufficient number of different data lines to equal the number of raster scan lines being used.
A digital memory for the data allows the picture on the TV screen to be frozen, allows easy interfacing with video tape and photograph equipment, allows instant storage of any image regardless of transducer movement, and allows a variable gray scale display.
Another advantage of the present invention is that it is able to make a split screen presentation of the data. That is to say, part of the screen can be used to show one representation, such as the cross sectional picture of the examined object, and another portion of the screen can be used to produce an ECG signal, an A scan, a time gain compensation curve, time motion, or any one of a number of other related or independent representations. Both displays can then be photographed in a single frame of film with a camera, such as the DELTA-MAT manufactured by Ohio-Nuclear, Inc.
A unique method of dual encoding minimizes hardware required. In the present invention each transducer element requires two enable signals in order to be activated. The same hardware can be used to determine the timing and sequencing and provide a first enable signal to a plurality of elements and the second enable signal to select among this plurality of elements. This reduces the timing and sequencing hardware to a fraction of the hardware needed in a single encoding system.
A PROM based scan generator enables the present invention to select groups of transducer elements which can be activated from left to right, right to left, or most importantly, in a non-sequential manner. By activating the groups in a non-sequential manner, the present invention is able to improve picture quality by reducing spurious echoes and signals from the preceding ultrasonic pulse and decrease the time between actuating subsequent groups. Further, the PROM based scan generator allows the invention to alternate between different modes of activating the transducer elements and group of elements. The invention can alternate between the modes of actuation needed to produce selected displays of the split screen format.
Additionally, the present invention includes an improved display format for one dimensional displays, such as an A scan. The data received by the transducers would normally produce a series of discrete data values which would show up on a cathode ray tube, such as a TV screen, as a series of dots. To overcome this, the present invention includes a further interpolation possessing means which functions to connect the dots and turn the display into a continuous line.